1. Field of the Invention
The present invention relates to a secondary air supply device for an internal combustion engine and a method of controlling the secondary air supply device. More specifically, the present invention relates to a secondary air supply device for an internal combustion engine that actuates an electric air pump to supply secondary air at cold start, and to a control method of the secondary air supply device.
2. Description of the Related Art
Some internal combustion engines for vehicles, such as automobiles, are provided with a secondary air supply device to promote secondary combustion of exhaust air by supplying secondary air into an upstream portion of an exhaust pipe during cold start and similar situations to reduce unburned components (for example, HC and CO) in the exhaust air. The secondary air supply device may include, for example, a pump that pressurizes air and supplies the pressurized to the exhaust pipe of the internal combustion engine, a valve disposed in a secondary air supply path, and control means for controlling actuation of an electric air pump according to, for example, the coolant temperature or other appropriate parameters for the internal combustion engine.
Some conventional secondary air supply devices of this type supply fresh air in the atmosphere to the exhaust pipe by means of the electric air pump, for example. Such devices prevent excessive consumption of electricity by supplying secondary air until after a catalytic converter for purifying exhaust is activated to a certain level (see Japanese Patent Application Publication No. 6-74028 (JP-A-6-74028), for example).
There is also known a technique to reduce the size of an electric air pump by causing supercharged air to be drawn into the air pump in a supercharged engine (see Japanese Patent Application Publication No. 7-26946 (JP-A-7-26946), for example).
In control devices for the conventional vehicles described above, however, the inrush current into the electric air pump may become so large as to cause a temporary excessive drop in the battery voltage, particularly if both the temperature is low and the battery is degraded. As a result, the load on an alternator may increase suddenly and the battery may be degraded easily.
As a countermeasure, it is conceivable to increase the size of the alternator and/or the battery, for example. However, some vehicles may not be able to accommodate a large alternator and/or a large battery. In addition, leaving power management to a power management ECU (electronic control unit) to manage a high-current system (an ECU for power management for a control system of various ECUs mounted on the vehicle that consume a high current and for determining whether to actuate each ECU, the order of actuation, and so on) increases the cost to set up the power management ECU.
Meanwhile, a vehicle stability control system or an electronically controlled brake system may be reset, or a meter or headlights may be turned on and off, if the operating voltage of an internal microcomputer of ECUs for vehicle stability control, braking control, display control, and so on is not maintained. Therefore, it is necessary to restrict an excessive drop in the voltage of the battery powering the ECUs.
Further, the recent demand for high exhaust gas purification performance on vehicles has increased the needs to increase the size of the electric air pump for supplying secondary air, and therefore it has become important to reduce the inrush current into the electric air pump.